The second and final phase of typical development to improve flow over standard.
In part 1, I carried out a series of preliminary tests, basic modifications and flowtests to establish the potential of the inlet port on the Fiat TC 1592cc cylinder head - things like testing the bare port flow and manifold flow, improvement to the short side radius, opening out to valve correct seat diameter, opening out the valve throat. In this section we'll see how these steps are taken further and how the port - chamber region of the inlet side is fully developed and checked ready for building-up.

Attachments

Deshrouding the chamber adjacent the inlet valve. The highest lift flow (See graph, part 1) is a long way from bare port flow. After this mod flow drops, a sign that the short-side radius may be wrong.

013 DT 1592 prelim deshroud.jpg (39.38 KiB) Viewed 17823 times

The cast-iron inlet seat will interfere with the machining of the head face so I'll need to recess it by grinding down the top edge into the alloy.

Pressing a GC race guide in the development port, head has been warmed to about 50 deg C and the the guide bores in the head lubricated with copper-based anti-seize.

018 DT 1592 race guide fitting.jpg (37.66 KiB) Viewed 16872 times

View to the port fully finished at 80 grit and the aerodynamically superior race guide in place. The bare port flow is now 102.6cfm compared with 91.1 standard, nearly 13% more, my average for a good job with 42mm valves.

The guides have to be checked after fitting, valve must drop under its own weight and be a snug fit. I use brush hones to correct any tight sports - which there usually are on old heads - even with perfect guides.

Alloy available for refacing is now just visible at the '6 o'clock' position of the inlet seat insert. Of course this takes the valve deeeper into the head, can present shiming problems for the unwary..

This job allows me assess whether I can shim it or not. If I've done my seats well, even by eye, tips should be very close to each other. I can grind valve tips to equalise, sometimes necessary if one seat/valve has been extensively reground due to wear/c

If you're good with seats this is how close you can get them. Std tip heights are about 40.5mm inlet and exhaust. This is common to sohc and 16v too - they share the same spring and spring seat.

041 DT 1592 tip hts measured.jpg (109.8 KiB) Viewed 16729 times

Final Test 31 spec, poor perfomance of POS valve and superior response of 30 deg top grind visible. It's can be hard to get valve-in flow closer to bpf in the 8v TC, you sometimes have to lift 13mm or more. Way better than standard though.

DT 1592 inlet flowtests phase_03.jpg (73.05 KiB) Viewed 16563 times

The top grind is better than 20 deg and best left sharp as this chart shows. It's something I only looked at quite recently, I think the 30 top grind interacts with the 30 deg back grind.